Versatile Technique to Produce a Hierarchical Design in Nanoporous Gold
February 10th, 2023
Nanoporous gold with a hierarchical and bimodal pore size distribution can be produced by combining electrochemical and chemical dealloying. The composition of the alloy can be monitored via EDS-SEM examination as the dealloying process advances. The material's loading capacity can be determined by studying protein adsorption onto the material.
Our protocol provides a method to produce nanoporous gold electrodes with hierarchical pore size distribution of larger pores for enhanced transport of molecules and smaller pores for increased surface area. The main advantage of the stepwise protocol lies in the strict control over the silver dissolution rate during de-alloying, which determines the electrode's final morphology. The healthcare system may benefit from the produced electrode design.
A faster and more precise diagnosis will be possible as the bimodal porous structure provides large surface area and easy movement of molecules. To begin, assemble an electrochemical cell in a five milliliter beaker. Use a Teflon-based lid with three holes to contain the three-electrode setup.
Place a platinum wire as a counter electrode, silver chloride as a reference electrode, and a gold wire as a working electrode in each lid hole maintaining a distance of 0.7 centimeters between the working and counter electrode. Prepare 50 millimolar solutions of each potassium silver cyanide and potassium gold cyanide in water. Add 0.5 milliliters of potassium gold cyanide solution and 4.5 milliliters of potassium silver cyanide salt solution in the five milliliter beaker.
Insert the magnetic stir bar into the electrochemical cell and mix the solution at 300 RPM stirring speed until the bubbling of argon gas is observed. Circulate argon gas through the electrolyte solution to remove dissolved oxygen using a silicone tube. Once the electrochemical cell is assembled, connect the potentiostat with alligator clips attached to the appropriate electrodes.
After turning on the potentiostat, use the software to perform electrode deposition utilizing chronoamperometry. Configure the software with the desired parameters. Set the potential at a fixed value of minus one volts for 600 seconds.
Press Run to complete the alloy deposition on the working electrode. For de-alloying, configure the electrochemical cell as previously demonstrated and use four milliliters of one normal nitric acid as the electrolyte solution for partial de-alloying. Once the solution is evenly circulated and the potentiostat is attached to the correct electrode, in the chronoamperometry software, set a potential of 0.6 volts for 600 seconds.
Press Run to finish de-alloying the deposited alloy on the working electrode. For the annealing process, keep the de-alloyed wires in a glass vial. Turn on the furnace, place the glass vial inside the furnace, and set the temperature at 600 degrees Celsius for three hours.
Once the process is finished, turn off the furnace, remove the vial, and let it cool to room temperature. For complete de-alloying, immerse the partially de-alloyed annealed wire in four milliliters of concentrated nitric acid and leave it in the fume hood overnight. The next day, remove the nitric acid from the vial.
Then prepare the hierarchical bimodal nanoporous gold or hierarchical bimodal MPG-coated wires by rinsing them with deionized water, followed by ethanol. After drying, visualize the wire using scanning electron microscopy. The scanning electron micrographs of hierarchical bimodal MPG demonstrated an open linked network of ligaments and pores following chemical de-alloying.
The larger holes were indicated by an upper hierarchy and the lower hierarchy indicated smaller pores. Color-coded elemental mapping for each step of the creation of hierarchical bimodal MPG revealed the presence of silver and gold. The cyclic voltammogram shown as an inset depicts the 10%gold in 90%silver alloy.
The structure created via chemical de-alloying showed a small gold oxide reduction. The bimodal structure incorporating chemical and electrochemical de-alloying showed a more pronounced gold oxide reduction peak, indicating an increase in the surface area. It is important to follow the sequential order of the protocol starting from alloying, de-alloying, annealing, chemical de-alloying, and strict control over the time and potential during alloying and de-alloying is equally important.
This method has made it possible to create electrochemically hierarchical designs and it can be expanded in the future to turn into a monolith for industrial use and create electrochemical biosensors for glycoproteins.
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Overview
This study presents a method for producing nanoporous gold electrodes with a hierarchical and bimodal pore size distribution. The unique structure enhances molecular transport and increases surface area, which could significantly benefit healthcare diagnostics.
Key Study Components
Area of Science
- Nanomaterials
- Electrochemistry
- Biomedical Engineering
Background
- Nanoporous materials have applications in various fields, including sensors and catalysis.
- Hierarchical pore structures can improve the performance of electrodes.
- Control over pore size distribution is crucial for optimizing material properties.
- The method involves electrochemical and chemical dealloying techniques.
Purpose of Study
- To develop a protocol for creating nanoporous gold electrodes.
- To enhance the transport of molecules through controlled pore sizes.
- To improve the surface area for better protein adsorption.
Methods Used
- Assembly of an electrochemical cell in a beaker.
- Use of a Teflon-based lid for a three-electrode setup.
- Monitoring the silver dissolution rate during de-alloying.
- Characterization of the alloy composition via EDS-SEM examination.
Main Results
- Successful production of nanoporous gold with desired pore characteristics.
- Demonstrated increased loading capacity through protein adsorption studies.
- Confirmed that the bimodal structure facilitates faster molecular movement.
- Potential applications in healthcare for improved diagnostic methods.
Conclusions
- The developed electrodes show promise for enhanced diagnostic capabilities.
- Control over pore size distribution is key to optimizing electrode performance.
- Further research may explore additional applications in biomedical fields.
